To ensure a safe system, most electrical equipment is equipped with an electrical fuse. When electrical wires are accidently shorted, a high current will flow locally. This can be avoided by an electrical fuse, shutting down the system when the current becomes higher than the expected current during normal use.
Electrical fuses are not effective for some types of lighting system, for example lighting systems consisting of a large number of lights (such as LEDs) connected to form a large wired network. Examples of this type of lighting systems are wearable lighting applications or sleeping bags equipped with lighting.
There are two reasons why this type of lighting system requires a different safety system. First of all, the resistance of multiple LEDs connected in series while turned ON is low and can even be comparable to the internal resistance of the wires. As a consequence, the total current during normal operation can be similar to the total current in the case of a short, making it difficult to detect shorts. For this reason, a regular fuse is not an effective safety feature.
The second reason why a fuse is not always effective arises when the LEDs are controlled individually. In this case, the resistance of the total system is strongly dependent on the number of LEDs that are turned on. Thus, for a system which is configurable in different ways, the required fuse current cannot easily be set.
Even if a normal operation has only a small number of LEDs turned on, a large fuse is still needed to allow the extraordinary case when all LEDs are turned on for a short time. This makes it difficult to limit the current through the system.
Electrical lighting circuits that are worn close to the body can present safety risks. For example, when the electrical wiring or the LEDs fail, the power dissipation can locally increase. This can result in local hot spots, which can harm the skin, or even ignite flames of the textile clothing.